INTRODUOTION, 13 
broader variety is before me ; it is also smooth like the first-named 
shell, and we have a corresponding variation of form in the variety 
N. foveolata, D’k’r., Martini and Chemnitz, 2nd. ed., pl. 6, f. 1, 2, 3, 
having an intermediate form in the shell figured by Reeve at pl. 13, 
f. 83. While some of the shells are broader than many of their 
more favoured figured brethren, others are much more elongated 
and narrower. A close alliance exists between the varieties of 
these shells and the varieties of the N. succincta, A. Ad., both as 
regards form, colour, and sculpture. The N. exilis, Powis, may be 
only a stronger ribbed variety. Some of the narrow shells 
belonging to the -N. marginulata, Lam., and N. sequijorensis, 
A. Ad., completely amalgamate with them, and the N. corniculum, 
Olivi, has many points of resemblance with them. In 
the N. crispata, Marr., the whole surface is covered with crisp 
longitudinal and transverse lines, being closely covered with 
granules in one variety, showing the knotted structure in a second, 
and a third shows a curious series of concentric rings, closely 
studded with elongated semi-tubercular longitudinal short ribs. 
I could make any number of good species, and, as Lamarck often 
exclaims, they shall be jolie et tres distincte, but I must then carefully 
avoid letting my collection be seen by any conchologist afterwards, 
more particularly by one who has a critical eye in his head, because 
he would detect the fraud. A case in point has just occurred to 
me. Examining some shells of N. picta, D’k’r., figured and 
described by conchologists as having a smooth columella, I found 
that some of them have the columella strongly plicate. Here, then, 
is a character that would serve to distinguish it, so that a child 
could detect it ; but unfortunately, the comparison instituted between 
the smooth and the plicate varieties revealed all the intermediate 
stages between the one and the other. Suppose these two extremes 
had accidentally fallen into the hands of a species maker, this 
apparent distinction would satisfy any number of his followers as 
far as relates to the distinguishing marks of the two species. 
These observations regarding the sculpture are a continuation 
of those enumerated in my former paper on the Variation of Sculp- 
ture. They differ more in the detail than in any other respect, and 
